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  #16 (permalink)  
Old 05-02-2012, 10:56 PM
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my KARMA ran over my DOGMA
 

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Quote:
Originally Posted by Silver Surfer
I believe I read it is a two-fold problem. The early Vortec heads used 6 intake manifold bolts on each side (new heads use 8). And I believe the plastic on the gasket cracked.
6 per side on the popular 062/906 head. Lots of intake leaks with standard thickness performance gasket, the factory gasket is .125 me thinks

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  #17 (permalink)  
Old 05-02-2012, 10:59 PM
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I don't do this for a living but in the past 3 years I've done 4 vortec engines, all four f them had spun rods. When I called posters on cl about their engines the badones were always a spun bearing, and only one was a main. As far as what the big tghree use its far more cost based than performance, they've been that way for a LONG time. Also, the factory redlines on those engines aren't too high, usually rods fail in tension, which depends on weight and rpm.

I put what I knew and I stand by it, and so far the only thing I've heard as an argument is "but the big three do it!" That means little more than the bean counters liked it.

Bash me all you want it won't do you a damn bit of good when you spin a bearing though.
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  #18 (permalink)  
Old 05-02-2012, 11:13 PM
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Quote:
Originally Posted by cool rockin daddy
Do whatever you want, AP. I mean, my god, you're all of 25 and you've built thousands of engines and of course you know more than the GM, Ford, and Chrysler metallurgy and con rod engineers put together. I mean, they're using them in DIESELS. Chrysler's 392 hemi has, ta-daa, pm con rods. But your comment about pm rods distorting more than a conventional rod says everything we need to know about your "expertise".

But gosh, I really do appreciate you slumming around here and gracing us with your presence yet again when you could be hanging around the geniuses at speedtalk. I really thought we had cured you of your attitude a few years back but it looks like it didn't stick.
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  #19 (permalink)  
Old 05-02-2012, 11:17 PM
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my KARMA ran over my DOGMA
 

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I would think that spinning a bearing has more to do with how its put together than whether its PM rod or not? What is the issue here?
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  #20 (permalink)  
Old 05-03-2012, 06:19 AM
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Quote:
Originally Posted by Custom10
I would think that spinning a bearing has more to do with how its put together than whether its PM rod or not? What is the issue here?
the issue is the big end flexes and distorts out of round.
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  #21 (permalink)  
Old 05-03-2012, 06:46 AM
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Quote:
Originally Posted by ap72
the issue is the big end flexes and distorts out of round.

Proof? What rpm does this happen? What equipment was used to measure? Who did the measuring?

Tell me how that happens in a pm rod that is FORGED, just like a other rods. Tell me how that happens given the comparison data from the Metaldyne article. You know, the company that has been supplying rods to the OEMs for decades.
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  #22 (permalink)  
Old 05-03-2012, 02:44 PM
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Quote:
Originally Posted by cool rockin daddy
Proof? What rpm does this happen? What equipment was used to measure? Who did the measuring?

Tell me how that happens in a pm rod that is FORGED, just like a other rods. Tell me how that happens given the comparison data from the Metaldyne article. You know, the company that has been supplying rods to the OEMs for decades.
PM is not forged like other rods, true enough it gets forged but how it starts is very different. The classic forged rod starts life as solid piece of material. This is usually hot rolled plate or from a bloom or ingot, work pieces are cut from the parent, they are heated to a red/orange heat, then placed between dies of an extremely powerful press and then are hammered into the dies. They are then cooled in a prescribed manner and finish machined. The big end may be made in one or two pieces. When made as part of the shank forging the cap is cut off with a saw (this is part the PM advertisers show you with the rough cut surface) what they eliminate from their advertising is that the big end of the shank and the cap are then finish machined to extremely close tolerances. High end rods it is often difficult to even see the parting line.

The PM rod starts out from a pile of metallic powder with inhibitors and fluxes not unlike the stuff wrapped around electric welding rods. It's poured into a mold and heated to a red/orange temp and the molds are pressed together to form the part. Like the from a blank made forging, the shank and cap can be made separately or together. When made together the big end is put in a fixture where enough force is applied to bust the cap off. At this the point where I have two problems: 1) I don't trust what the fracture forces do to the underlying metallic structure in and around the fracture zone. 2) And going with my experience with what are called near net forgings and castings, that when these required finish machining we got in service distortions from those areas where the compressed skin of the forging or casting was thinned or removed. Removal or relief of the compressed surface is a big issue, you see an immediate deformation in the fracture zone because the surface of the compressed material expands as internal stresses relieve themselves through this surface. Of the spun bearing failures I've seen with the PM rod production engines, I'm of the opinion that self stress relieving in the fracture zone is the Root Cause. With these PM metals the malleability of the material seems to have a random sensitivity which is probably related to the powder mix and/or heat and/or forging forces and/or post part cooling and subsequent processes. Which I suspect is why the type of failure AP72 sights seems random and infrequent, but has a background consistency about it at the same time.

I understand that forging from blanks carries it's own problems where decarburaztion, inclusions and various chemical and structural issues cause problems with the end part, but powder forging is by no means free of many of these defects and adds a few new ones of their own.

As long as I can avoid PM rods I intend to do so, they strike me as a cost reduction issue to the OEM more than a technology improvement for performance. I suppose that in low rate production and with careful part examination they can be made suitable for performance work with high reliability, but looking at OEM production rates, I certainly wouldn't trust my performance engine to these. But then I don't trust to production forged steel rods, including pinks, either.

Bogie
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  #23 (permalink)  
Old 05-03-2012, 11:44 PM
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1.21 giga-watts???!!!!
 
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Thank you, bogey. Since I work in the metal cutting industry I am very well versed in sintered metals, forging vs. casting, etc. It was a well written piece that I am sure educated a great many people. However, I, as well as others, are waiting for the proof to back up what the "26 year old of a thousand engines" has said about rods in general. I want the stats, who came up with them, how were they derived, what kind of equipment was used to measure, etc. See, this bit about pm rods being inferior is no different than the wive's tale that GM "pink" rods were something special. Really shouldn't be that hard to come up with the SCIENTIFIC proof of what he spouted off. Should it?
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  #24 (permalink)  
Old 05-04-2012, 01:52 AM
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One thing I believe is worth noting about ap72's (or anyone's for that matter) non scientific semi-empirical evidence regarding a mode of failure that's attributed to a perceived design flaw of PM rods in general and the Vortec L31 engine PM rods in particular, is the sample population.

In the case of ap72, it would seem he's basing his observations on a VERY narrow segment, i.e. cheap core engines that are blown up.

The problem with stating categorically that a PM rod was the root cause of a failure (and not merely collateral damage) is that w/o witnessing the failure, or making a close, precise examination of the failed engine in total, along w/a really good grasp of metallurgy and related sciences involving stress analysis, along w/the necessary equipment to measure the properties of the rod itself and to view the failed components in enough detail that other causes can be absolutely ruled out, there can be no real way for a layman to say w/any amount of certainty that the PM rod material/design/manufactute is at fault.

To the average observer, there is just no way to state w/certainty it was the rod that's at fault and not the rod fasteners, or a deficency in the oil, oil clearances, or oiling system, or the engine was severely over revved or in some other way operated in excess of its design limitations, or was assembled wrong in any of a hundred ways, et cetera.

The bottom line for me is I believe if a larger segment/population were to be used to make a similar "study", one may well find that PM rods do not fare as poorly as it might seem when only looking at blown up, cheap core engines.
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  #25 (permalink)  
Old 05-04-2012, 07:57 AM
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Quote:
Originally Posted by cool rockin daddy
Thank you, bogey. Since I work in the metal cutting industry I am very well versed in sintered metals, forging vs. casting, etc. It was a well written piece that I am sure educated a great many people. However, I, as well as others, are waiting for the proof to back up what the "26 year old of a thousand engines" has said about rods in general. I want the stats, who came up with them, how were they derived, what kind of equipment was used to measure, etc. See, this bit about pm rods being inferior is no different than the wive's tale that GM "pink" rods were something special. Really shouldn't be that hard to come up with the SCIENTIFIC proof of what he spouted off. Should it?
I never claimed a thousand engines, I've never counted but including basic stock rebuilds I'm probably only around 50 engines total.

As for your scientific proof I could go through the effort of doing that but unlike bogey I don't work for free. Ill give 5-10 minutes to a post but beyond that its not worth my time IMO.

Some people don't mind dedicating time to long posts or wiki articles or how to videos and pictorial walk throughs, I appreciate their efforts but I have better things to do. Id like to do one pictorial walk through some day to "give back" to those that helped me but that's where my generous nature ends.

This is a free internet forum that allows anyone to post, which is wonderful in a lot of respects, but not worth more than a few thoughts.
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Old 05-04-2012, 08:25 AM
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Last edited by cobalt327; 05-04-2012 at 08:34 AM. Reason: Totally not worth MY time.
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  #27 (permalink)  
Old 05-04-2012, 08:32 AM
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There are SAE papers detailing the advantages of PM over forged for production engines, but I dont know what it takes to get access to the archive.
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  #28 (permalink)  
Old 05-04-2012, 08:45 AM
How fast is fast enough?
 
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Quote:
Originally Posted by lmsport
There are SAE papers detailing the advantages of PM over forged for production engines, but I dont know what it takes to get access to the archive.
There are also a lot of discussions and related articles on speedtalk like I already said, anyone can become a member there.
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  #29 (permalink)  
Old 05-04-2012, 04:01 PM
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1.21 giga-watts???!!!!
 
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Quote:
Originally Posted by ap72
I never claimed a thousand engines, I've never counted but including basic stock rebuilds I'm probably only around 50 engines total.

As for your scientific proof I could go through the effort of doing that but unlike bogey I don't work for free. Ill give 5-10 minutes to a post but beyond that its not worth my time IMO.

Some people don't mind dedicating time to long posts or wiki articles or how to videos and pictorial walk throughs, I appreciate their efforts but I have better things to do. Id like to do one pictorial walk through some day to "give back" to those that helped me but that's where my generous nature ends.

This is a free internet forum that allows anyone to post, which is wonderful in a lot of respects, but not worth more than a few thoughts.

Money talks, bullroar walks. The above is the typical response of somebody that can't back up what he says. "I don't work for free", "I don't have the time" blah, blah, blah. Please, just stay over there at speedtalk, whatever that is. Just because a site is free doesn't give one license to post pure bunk with no corroborating facts. Maybe that's what flies over there but this site needs to be rid of it.
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  #30 (permalink)  
Old 05-04-2012, 04:56 PM
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Quote:
Originally Posted by cool rockin daddy
............over there at speedtalk, whatever that is.

The Speed Talk website has a forum geared more to professional builders and machinists than general subjects. Another source of very good info with a bit of a different "flavor" than HotRodders. I like both.

Ed
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